Plant Pathology Graduate Program

Howard S. Judelson

Howard S. Judelson
Office: 951-827-4199
1231 Genomics Building
Office Hours: , not specified - not specified
Email: howard.judelson@ucr.edu

Howard S. Judelson

Professor of Plant Pathology

Molecular biology and genomics of oomycetes, with an emphasis on the biology and pathology  of Phytophthora infestans



Postdoctoral training, University of California-Davis

PhD in Molecular Biology, University of Wisconsin-Madison 

BS in Biochemistry, Cornell University


Biography & Research Interests


Our laboratory studies the eukaryotic microbe Phytophthora infestans, which is responsible for the late blight diseases of tomato and potato.  This "fungus-like" organism, more properly classified as an oomycete or water mold, causes billions of dollars of losses annually and is a major threat to global food security.  In the long term, our work will lead to a greater understanding of oomycetes and help develop strategies for controlling them.

Most of our research involves characterizing genes and proteins involved in the growth and pathogenesis of P. infestans, particularly those involved in forming spores and infection structures.  Our work is multidisciplinary and involves genetics, genomics, proteomics, cell biology, biochemistry, and pathology.  For example, we have developed genome sequences of P. infestans and used that data to identify genes important in pathogenesis, to identify regulatory networks that control progression through the life cycle, and to understand the evolutionary history of P. infestans and its relatives. 

We also have pioneered the development of transformation-based methods for manipulating genes in P. infestans, and continue to advance those techniques.  For example, we have developed collections of fluorescent protein fusion vectors that are used by the oomycete research community.

Several of our projects involve collaborations with Cooperative Extension and other field-based personnel, as we translate our findings to practical solutions for growers.

More information about the lab and our research activities can be found at the Judelson lab website at: oomyceteworld.net.


    • Ruth Allen Award, American Phytopathological Society
    • Fellow, American Association for the Advancement of Science
    • Fellowship, National Institutes of Health
    • Fellowship, McKnight Foundation
    • Ho-Nun-De-Kah


(since 2000)

Abrahamian M, Ah-Fong AMV, Davis C, Andreeva K, Judelson HS. 2016. Gene Expression and Silencing Studies in Phytophthora infestans Reveal Infection-Specific Nutrient Transporters and a Role for the Nitrate Reductase Pathway in Plant Pathogenesis. PLoS Pathogens 12: e1006097.

Knaus, B., Tabima, J., Davis, C., Judelson, H.S., Grunwald, N. 2016. Genomic Analyses of Dominant U.S. Clonal Lineages of Phytophthora infestans Reveals a Shared Common Ancestry for Clonal Lineages US11 and US18 and a Lack of Recently Shared Ancestry Among All Other U.S. Lineages. Phytopathology 106:1393-1403.

Hansen, Z., Everts, K., Fry, W., Gevens, A., Grunwald, N., Gugino, B., Johnson, D., Johnson, S., Judelson, H.S., Knaus, B., McGrath, M., Myers, K., Ristaino, J., Roberts, P., Secor, G., Smart, C. 2016. Genetic Variation within Clonal Lineages of Phytophthora infestans Revealed through Genotyping-By-Sequencing, and Implications for Late Blight Epidemiology. Plos One. 11:e0165690.

Hansen, Z., Knaus, B., Tabima, J., Press, C., Judelson, H., Grunwald, N., Smart, C. 2016. Loop-Mediated Isothermal Amplification (LAMP) for Detection of the Tomato and Potato Late Blight Pathogen Phytophthora infestans. Journal of Applied Microbiology 120:1010-1020.

Hansen, Z., Knaus, B., Tabima, J., Press, C., Judelson, H.S., Grunwald, N., Smart, C. 2016. SNP-based differentiation of Phytophthora infestans clonal lineages using locked nucleic acid probes and high resolution melt analysis. Plant Disease 100:1297-1306.

Poidevin L, Andreeva K, Khachatoorian C, Judelson HS. 2015. Comparisons of ribosomal protein gene promoters indicate superiority of heterologous regulatory sequences for expressing transgenes in Phytophthora infestans. PloS One 2015 10: e0145612.

Sharma, R., Xiaojuan, X., Cano, L., Evangelisti, E., Kemen, E., Judelson, H., Oome, S., Sambles, C., van den Hoogen, D., Kitner, M., Meijer, H., Spring, O., Win, J., Zipper, R., Bode, H., Govers, F., Kamoun, S., Schornack, S., Studholme, D., van den Ackerveken, G., Thines, M. 2015. Genome analyses of the sunflower pathogen Plasmopara halstedii provide insights into effector evolution in downy mildews and Phytophthora . BMC Genomics. 16: e741.

Matson M.H.E., Small I, Fry WE, Judelson HS. 2015. Metalaxyl resistance in Phytophthora infestans: assessing role of RPA190 gene and diversity within clonal lineages. Phytopathology 105:1594-600. 

Fry, W., P. Birch, H. Judelson, N. J. Grünwald, G. Danies, K. L. Everts, A. J. Gevens, B. Gugino, D. A. Johnson, S. B. Johnson, M. McGrath, K. L. Myers, J. B. Ristaino, G. A. Secor and C. D. Smart. 2015.  Five reasons to consider Phytophthora infestans a reemerging pathogen.  Phytopathology, 105:966-81.

Kamoun, S., Furzer, O., Jones, J. D. G., Judelson, H. S., Ali, G. S., Dalio, R. J. D., Roy, S. G., Schena, L., Zambounis, A., Panabières, F., Cahill, D., Ruocco, M., Figueiredo, A., Chen, X.-R., Hulvey, J., Stam, R., Lamour, K., Gijzen, M., Tyler, B. M., Grünwald, N. J., Mukhtar, M. S., Tomé, D. F. A., Tör, M., Van Den Ackerveken, G., McDowell, J., Daayf, F., Fry, W. E., Lindqvist-Kreuze, H., Meijer, H. J. G., Petre, B., Ristaino, J., Yoshida, K., Birch, P. R. J. and Govers, F. 2015.  The Top 10 oomycete pathogens in molecular plant pathology. Molecular Plant Pathology, 16: 413–434.

Gamboa-Melendez H, Judelson HS. 2015.  Development of a bipartite chemical-inducible gene switch based on the ecdysone receptor for the oomycete Phytophthora infestans.  Molecular Plant Pathology 16: 83-91.

Xiang Q, Judelson HS. 2014. Myb transcription factors and light regulate sporulation in the oomycete Phytophthora infestans. PLoS ONE 9: e92086. 

Gamboa-Melendez H, Huerta A, Judelson HS. 2013.  bZIP transcription factors in the oomycete Phytophthora infestans with novel DNA-binding domains are involved in defense against oxidative stress.  Eukaryotic Cell 12: 1403-12.

W. E. Fry, M. T. McGrath, A. Seaman, T. A. Zitter, A. McLeod, G. Danies, I. M. Small, K. Myers, K. Everts, A. J. Gevens, B. K. Gugino, S. B. Johnson, H. Judelson, J. Ristaino, P. Roberts, G. Secor, K. Seebold, Jr., K. Snover-Clift, A. Wyenandt, N. J. Grünwald, and C. D. Smart. 2013. The 2009 Late Blight Pandemic in the Eastern United States, Causes and Results. Plant Disease 97: 296-306.

Roy S, Kagda M, Judelson HS. 2013. Genome-wide Prediction and Functional Validation of Promoter Motifs Regulating Gene Expression in Spore and Infection Stages of Phytophthora infestans. PLoS Pathogens 9:e1003182.

Roy S, Poidevin L, Jiang T, Judelson HS. 2013. Novel core promoter elements in the oomycete pathogen Phytophthora infestans and their influence on expression detected by genome-wide analysis. BMC Genomics 14:106.

Qiao Y, Liu L, Xiong Q, Flores C, Wong J, Shi J, Wang X, Liu X, Xiang Q, Jiang S, Zhang F, Wang Y, Judelson HS, Chen X, Ma W. 2013. Oomycete pathogens encode RNA silencing suppressors.  Nature Genetics 45:330-333.

Judelson HS, Shrivastava J, Manson J. 2012.  Decay of genes encoding the oomycete flagellar proteome in the downy mildew Hyaloperonospora arabidopsidis.  PLoS One 7:e47624.

Judelson HS.  2012.  Dynamics and innovations within oomycete genomes: insights into biology, pathology, and evolution.  Eukaryotic Cell 11:1304-1312.

Ah-Fong AM, Judelson HS. 2011. Vectors for fluorescent protein tagging in Phytophthora: tools for functional genomics and cell biology. Fungal Biology 115:882-890.

Ah-Fong AM, Judelson HS. 2011.  New role for Cdc14 phosphatase: localization to basal bodies in the oomycete Phytophthora and its evolutionary coinheritance with eukaryotic flagella.  PLoS One 6:e16725.

Baxter L, Tripathy S, Ishaque N, Boot N, Cabral A, Kemen E, Thines M, Ah-Fong A, Anderson R, Badejoko W, Bittner-Eddy P, Boore JL, Chibucos MC, Coates M, Dehal P, Delehaunty K, Dong S, Downton P, Dumas B, Fabro G, Fronick C, Fuerstenberg SI, Fulton L, Gaulin E, Govers F, Hughes L, Humphray S, Jiang RH, Judelson H, Kamoun S, Kyung K, Meijer H, Minx P, Morris P, Nelson J, Phuntumart V, Qutob D, Rehmany A, Rougon-Cardoso A, Ryden P, Torto-Alalibo T, Studholme D, Wang Y, Win J, Wood J, Clifton SW, Rogers J, Van den Ackerveken G, Jones JD, McDowell JM, Beynon J, Tyler BM.  2010.  Signatures of adaptation to obligate biotrophy in the Hyaloperonospora arabidopsidis genome.  Science 330:1549-51. 

Judelson HS, Ah-Fong AM. 2010. The kinome of Phytophthora infestans reveals oomycete-specific innovations and links to other taxonomic groups. BMC Genomics 11:700.

Judelson HS, Ah-Fong AM, Fabritius AL. 2010.  An RNA symbiont enhances heat tolerance and secondary homothallism in the oomycete Phytophthora infestans. Microbiology 156:2026-2034.

Xiang Q, Judelson HS. 2010.  Myb transcription factors in the oomycete Phytophthora with novel diversified DNA-binding domains and developmental stage-specific expression. Gene 453:1-8.

Haas BJ, Kamoun S, Zody MC, Jiang RH, Handsaker RE, Cano LM, Grabherr M, Kodira CD, Raffaele S, Torto-Alalibo T, Bozkurt TO, Ah-Fong AM, Alvarado L, Anderson VL, Armstrong MR, Avrova A, Baxter L, Beynon J, Boevink PC, Bollmann SR, Bos JI, Bulone V, Cai G, Cakir C, Carrington JC, Chawner M, Conti L, Costanzo S, Ewan R, Fahlgren N, Fischbach MA, Fugelstad J, Gilroy EM, Gnerre S, Green PJ, Grenville-Briggs LJ, Griffith J, Grünwald NJ, Horn K, Horner NR, Hu CH, Huitema E, Jeong DH, Jones AM, Jones JD, Jones RW, Karlsson EK, Kunjeti SG, Lamour K, Liu Z, Ma L, Maclean D, Chibucos MC, McDonald H, McWalters J, Meijer HJ, Morgan W, Morris PF, Munro CA, O'Neill K, Ospina-Giraldo M, Pinzón A, Pritchard L, Ramsahoye B, Ren Q, Restrepo S, Roy S, Sadanandom A, Savidor A, Schornack S, Schwartz DC, Schumann UD, Schwessinger B, Seyer L, Sharpe T, Silvar C, Song J, Studholme DJ, Sykes S, Thines M, van de Vondervoort PJ, Phuntumart V, Wawra S, Weide R, Win J, Young C, Zhou S, Fry W, Meyers BC, van West P, Ristaino J, Govers F, Birch PR, Whisson SC, Judelson HS, Nusbaum C. 2009.  Genome sequence and comparative analysis of the Irish potato famine pathogen Phytophthora infestans. 2009. Nature 461:393-398.

Judelson, H.S., Narayan, R., Tani, S. 2009. Metabolic adaptation of Phytophthora infestans during growth on leaves, tubers, and artificial media. Molecular Plant Pathology 10, 843-855.

Xiang, Q., Roy, S., Kim, K., Judelson, H.S. 2009. A motif within a complex promoter from the oomycete Phytophthora infestans determines transcription during an intermediate stage of sporulation. Fungal Genetics and Biology 46: p.400-409.

Judelson, H. S., Narayan, R. D., Ah-Fong, A. M. V., and Kim, K-S. 2009. Gene expression changes during asexual sporulation by the late blight agent Phytophthora infestans occur in discrete temporal stages. Molecular Genetics and Genomics, 281, 193-206.

Ah-Fong, A. M. V., Bormann-Chung, C. A. and Judelson, H. S. 2008. Optimization of transgene-mediated silencing in Phytophthora infestans and its association with small interfering RNAs. Fungal Genetics and Biology 45, 1197-1205.

Ah-Fong, A. M. V., and Judelson, H. S. 2008. Molecular Strategies for Identifying Determinants of Oomycete Pathogenicity. Pages 383 to 410 in: Molecular Mechanisms of Plant and Microbe Coexistence (Nautiyal, C., and Dion, P. eds). Springer, Heidelberg.

H. S. Judelson, A. M. V. Ah-Fong, G. Aux, A. O. Avrova, C. Bruce, C. Cakir, L. da Cunha, L. Grenville-Briggs, M. Latijnhouwers, W. Ligterink, H. J.G. Meijer, S. Roberts, C. S. Thurber, S. C. Whisson, P. R. J. Birch, F. Govers, S. Kamoun, P. van West, and J. Windass. 2007. Gene expression profiling during asexual development of the late blight pathogen Phytophthora infestans reveals a highly dynamic transcriptome. Molecular Plant-Microbe Interactions 21, 433-447.

Ah-Fong, A. M.V., Xiang, Q., and Judelson, H. S. 2007. Architecture of the sporulation-specific Cdc14 promoter from the oomycete Phytophthora infestans. Eukaryotic Cell 6, 2222–2230.

Judelson, H. S. 2007. Sexual reproduction in plant pathogenic oomycetes: biology and impact on disease. Pages 445 to 458 In: Sex in fungi: molecular determination and evolutionary implications (J. Heitman, J. Kronstad, J. Taylor, L. Casselton, eds.). ASM Press, Washington DC.

Judelson, H. S., and Tani, S. 2007. Transgene-induced silencing of the zoosporogenesis-specific PiNIFC gene cluster of Phytophthora infestans involves chromatin alterations. Eukaryotic Cell 6, 1200-1209.

Judelson, H. S., Narayan, R., Ah Fong, A. M. V., Tani, S., and Kim, K. S. 2007. Performance of a tetracycline-responsive transactivator system for manipulating gene expression in the oomycete Phytophthora infestans. Current Genetics 51,297-307.

Prakob, W. and Judelson, H. S. 2007. Gene expression during oosporogenesis in heterothallic and homothallic Phytophthora. Fungal Genetics and Biology 44, 726-739.

Judelson, H. S. 2007. Genomics of the plant pathogenic oomycete Phytophthora: insights into biology and evolution. Advances in Genetics 57, 98-142.

Judelson, H. S., and Ah Fong, A. M. V. 2007. Genomics of oomycetes. Pages 1 to 4 in: Encyclopedia of Plant and Crop Science (R. Goodman, ed.), Taylor and Francis, New York.

Judelson, H. S., and Senthil, G. 2006. Investigating the role of ABC transporters in multifungicide insensitivity in Phytophthora infestans. Molecular Plant Pathology 7, 17-29.

Cvitanich, C., Salcido, M., and Judelson, H. S. 2006. Concerted evolution of a tandemly arrayed family of mating-specific genes in Phytophthora analyzed through interspecific and intraspecific comparisons. Molecular Genetics and Genomics275, 169-184.

Tani, S., and Judelson, H. S. 2006. Activation of zoosporogenesis-specific genes in Phytophthora infestans involves a seven-nucleotide promoter motif and cold-induced membrane rigidity. Eukaryotic Cell 42, 745-752.

Blanco, F.A., and H.S. Judelson. 2005. A bZIP transcription factor from Phytophthora interacts with a protein kinase and is required for zoospore motility and plant infection. Molecular Microbiology 56, 638-648.

Randall, T. A., Dwyer, R. A., Huitema, E., Beyer, K., Cvitanich, C., Kelkar, H., Ah Fong, A. M. V., Gates, K., Roberts, S., Yatzkan, E., Gaffney, T., Law, M., Testa, A., Torto, T. , Zhang, M., Zheng, L., Mueller, E., Windass, J., Binder, A. , Birch, P. R. J., Gisi, U., Govers, F., Gow, N. A., Mauch, F., van West, P., Waugh, M., Yu, J., Boller, T., Kamoun, S., Lam, S. T., and Judelson, H. S. 2005. Large-scale gene discovery in the oomycete Phytophthora infestans reveals likely components of phytopathogenicity shared with true fungi. Molecular Plant-Microbe Interactions 18:229-243

Tani, S., Kim, K.-S., and Judelson, H. S. 2005. A cluster of NIF transcriptional regulators with divergent patterns of spore-specific expression in Phytophthora infestans. Fungal Genetics and Biology 42, 42-50.

Judelson, H. S. and Blanco, F. A. 2005. The spores of Phytophthora: weapons of the plant destroyer. Nature Reviews Microbiology, 3:47-58

Ah Fong, A., and Judelson, H. S. 2004. The hAT-like DNA transposon, DodoPi, resides in a cluster of retro- and DNA transposons inthe stramenopile Phytophthora infestans. Molecular Genetics and Genomics 271, 577-585.

Tani, S., Yatzkan, E., and Judelson, H. S. 2004. Multiple pathways regulate the induction of genes during zoosporogenesis in Phytophthora infestans. Molecular Plant Microbe Interactions17, 330-337.

Kim, K., and Judelson, H. S. 2003. Sporangia-specific gene expression in the oomycete phytopathogen Phytophthora infestans. Eukaryotic Cell 2, 1376-1385.

Ah Fong, A., and Judelson, H. S. 2003. Cell cycle regulator Cdc14 is expressed during sporulation but not hyphal growth in the fungus-like oomycete Phytophthora infestans. Molecular Microbiology 50, 487-494.

Fabritius, A.-L. and Judelson, H. S. 2003. A mating-induced protein of Phytophthora infestans is a member of a family of elicitors with divergent structures and stage-specific patterns of expression. Molecular Plant-Microbe Interactions16, 926-935.

Cvitanich, C. and Judelson, H. S. 2003. A gene expressed during sexual and asexual sporulation in Phytophthora infestans is a member of the Puf family of translational regulators. Eukaryotic Cell 2, 465-473.

Cvitanich, C. and Judelson, H. S. 2003. Transformation of the oomycete, Phytophthora infestans, using microprojectile bombardment. Current Genetics 42, 228-235.

Judelson, H. S. 2002. Sequence variation and genomic amplification of a family of Gypsy-like sequences in the oomycete genus Phytophthora. Molecular Biology and Evolution 19, 1313-1322.

Judelson, H. S. and S. Roberts. 2002. Novel protein kinase induced during sporangial cleavage in the oomycetePhytophthora infestans. Eukaryotic Cell 1, 687-695.

Fabritius, A.-L., and Judelson, H. S. 2002. Stage-specific gene expression during mating in Phytophthora infestans. Molecular Microbiology 45, 1057-1066.

Randall, T. A., Ah Fong, A., and Judelson, H. S. 2002. Chromosomal heteromorphism and an apparent translocation detected using a BAC contig spanning the mating type locus of Phytophthora infestans. Fungal Genetics and Biology 38, 75-84.

Judelson, H. S., and Tooley, P. W. 2000. Enhanced PCR methods for detecting and quantifying Phytophthora infestans in plants. Phytopathology 90, 1112-1119.

Judelson, H. S., and Fabritius, A-L. 2000. A linear RNA replicon from the oomycete, Phytophthora infestans. Molecular and General Genetics 263, 395-403.

More Information

General Campus Information

University of California, Riverside
900 University Ave.
Riverside, CA 92521
Tel: (951) 827-1012

Career OpportunitiesUCR Libraries
Campus StatusDirections to UCR

Department Information

Department of Plant Pathology and Microbiology
Boyce Hall

Tel: (951) 827-3598
Fax: (951) 827-2364
E-mail: jammy.yang@ucr.edu